Led lighting systems with triac dimmers and methods thereof

ABSTRACT

System and method for controlling one or more light emitting diodes. For example, the system for controlling one or more light emitting diodes includes a current regulation circuit coupled to a cathode of one or more light emitting diodes. The one or more light emitting diodes include the cathode and an anode configured to receive a rectified voltage. Additionally, the system includes a control circuit coupled to the cathode of the one or more light emitting diodes. The control circuit is configured to receive a first voltage from the cathode of the one or more light emitting diodes, compare a second voltage and a threshold voltage, and generate a control signal based at least in part on the second voltage and the threshold voltage. The second voltage indicates a magnitude of the first voltage.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201711464007.9, filed Dec. 28, 2017, incorporated by reference hereinfor all purposes.

2. BACKGROUND OF THE INVENTION

Certain embodiments of the present invention are directed to circuits.More particularly, some embodiments of the invention provide lightingsystems and methods with Triode for Alternating Current (TRIAC) dimmers.Merely by way of example, some embodiments of the invention have beenapplied to light emitting diodes (LEDs). But it would be recognized thatthe invention has a much broader range of applicability.

As a new energy-saving and environmentally-friendly light source, lightemitting diode (LED) is widely used in various fields due to its highluminance, low power consumption and long life span. For example, withina range close to a rated current, luminance of an LED often is directlyproportional to the current flowing through the LED but is independentof the voltage across the LED; therefore, LED is often supplied withpower from a constant current source during operation.

FIG. 1 is an exemplary circuit diagram showing a conventional linearconstant current LED lighting system with a Triode for AlternatingCurrent (TRIAC) dimmer. The linear constant current LED lighting system100 is widely used in various fields such as LED lighting due to thesystem's simple and reliable structure and low cost. As shown in FIG. 1,the main control unit of the system 100 includes: an error amplifier U1,a transistor M1 for power regulation, and an LED current sensingresistor R1. The positive input terminal of the amplifier U1 receives areference voltage V_(ref), and the negative input terminal of theamplifier U1 is connected to the sensing resistor R1. Additionally, theoutput terminal of the amplifier U1 is connected to the gate terminal ofthe transistor M1 for power regulation.

As shown in FIG. 1, after the system 100 is powered on, an AC inputvoltage (e.g., VAC) is received by a TRIAC dimmer 190 and subjected to afull-wave rectification process performed by a full-wave rectifyingbridge BD1 to generate a rectified voltage 101 (e.g., V_(bulk)). Forexample, the rectified voltage 101 does not drop below 0 volt. Also,after the system 100 is powered on, the amplifier U1 of the main controlunit controls the voltage 103 of the gate terminal of the transistor M1,so that the transistor M1 is closed (e.g., the transistor M1 beingturned on). As an example, the voltage 101 (e.g., V_(bulk)) is higherthan a minimum forward operating voltage of the one or more LEDs, and acurrent 105 flows through the one or more LEDs to the sensing resistorR1 via the transistor M1.

The sensing resistor R1 includes two terminals. For example, oneterminal of the sensing resistor R1 is grounded, and another terminal ofthe sensing resistor R1 generates a voltage (e.g., V_(sense)). As anexample, the magnitude of the voltage (e.g., V_(sense)) across theresistor R1 corresponds to the current 105 flowing through the one ormore LEDs. The amplifier U1 receives the voltage V_(sense) at one inputterminal and receives the reference voltage V_(ref) at another inputterminal, and performs an error amplification process on the voltageV_(sense) and the reference voltage V_(ref) in order to adjust the gatevoltage 103 of the transistor M1 and realize constant current controlfor the one or more LEDs. The LED current I_(led) (e.g., the currentflowing through the one or more LEDs) is shown in Equation 1:

$\begin{matrix}{I_{led} = \frac{V_{ref}}{R_{1}}} & ( {{Equation}\mspace{14mu} 1} )\end{matrix}$

where R₁ represents the resistance of the resistor R1, and V_(ref)represents the reference voltage.

FIG. 2 shows simplified conventional timing diagrams for the LEDlighting system 100 as shown in FIG. 1. The waveform 210 represents therectified voltage V_(bulk) (e.g., the rectified voltage 101) as afunction of time, the waveform 220 represents the voltage of the gateterminal of the transistor M1 (e.g., the gate voltage 103) as a functionof time, and the waveform 230 represents the LED current I_(led) (e.g.,the current 105 flowing through the one or more LEDs) as a function oftime.

In certain TRIAC dimmer applications, the AC input voltage (e.g., VAC)is, for example, clipped by the TRIAC dimmer 190 and also rectified togenerate the rectified voltage 101 (e.g., V_(bulk)), which is receivedby an anode of the one or more LEDs. As shown by the waveform 210,during one or more time durations (e.g., from time t₁ to time t₂), therectified voltage 101 (e.g., V_(bulk)) either is larger than zero butstill small in magnitude or is equal to zero because the TRIAC dimmer190 operates in an off cycle, so that the voltage 101 (e.g., V_(bulk))is lower than the minimum forward operating voltage of the one or moreLEDs. For example, during the off cycle, the TRIAC dimmer 190 clips theAC input voltage (e.g., VAC) so that the rectified voltage 101 (e.g.,V_(bulk)) equals zero in magnitude. As an example, from time t₁ to timet₂, the one or more LEDs cannot be turned on due to insufficientmagnitude of the voltage 101 and the LED current I_(led) is equal tozero, as shown by the waveforms 210 and 230. At this point (e.g., at atime between time t₁ and time t₂), the constant current control circuitof FIG. 1 is still working. For example, the voltage V_(bulk) is low andno current flows through the one or more LEDs, so the voltage of thegate terminal of the transistor M1, which is provided by the outputterminal of the U1 amplifier, is at a high voltage level (e.g., at avoltage level V₂ from time t₁ to time t₂ as shown by the waveform 220).As an example, as shown by the waveform 220, prior to the time t₁, thevoltage of the gate terminal of the transistor M1 is at a low voltagelevel (e.g., at a voltage level V₁). For example, the voltage level V₂is higher than the voltage level V₁, and the voltage level V₁ is higherthan a threshold voltage of the gate terminal for turning on thetransistor M1.

As shown in FIG. 2, at time t₂, the TRIAC dimmer 190 enters an on cycle,during which, the TRIAC dimmer 190 does not clip the AC input voltage(e.g., VAC), as shown by the waveform 210. For example, at time t₂, theV_(bulk) voltage increases rapidly while the voltage of the gateterminal of the transistor M1 is at the high voltage level, causing theLED current I_(led) to overshoot, as shown by the waveforms 210, 220 and230. During the loop adjustment process for constant current of the LEDlighting system 100, after overshoot of the LED current I_(led), thereis an oscillation period (e.g., from time t₂ to time t3) as shown by thewaveforms 220 and 230.

As discussed above, a resulting problem of the LED lighting system 100is that the change in the V_(bulk) voltage caused by the TRIAC dimmer190 can cause overshoot and oscillation of the LED current I_(led). Forsome TRIAC dimmers, this type of current overshoot and oscillation mayeven cause the TRIAC dimmer (e.g., the TRIAC dimmer 190) to operateabnormally (e.g., causing the TRIAC dimmer 190 to misfire), which inturn causes abnormal fluctuations in the LED current I_(led) and causesthe one or more LEDs to flicker.

Hence it is highly desirable to improve techniques related to LEDlighting systems with TRIAC dimmers.

3. BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the present invention are directed to circuits.More particularly, some embodiments of the invention provide lightingsystems and methods with Triode for Alternating Current (TRIAC) dimmers.Merely by way of example, some embodiments of the invention have beenapplied to light emitting diodes (LEDs). But it would be recognized thatthe invention has a much broader range of applicability.

Some embodiments of the present invention provide a high-compatibilityTRIAC dimmer control system for an LED lighting system and a method ofusing such switch control system. For example, the TRIAC dimmer controlsystem eliminates current overshoot and oscillation caused by a suddenchange of a rectified voltage during a TRIAC dimming process bycontrolling enablement of a constant current circuit of the system. Asan example, the TRIAC dimmer control system prevents a TRIAC dimmer fromoperating abnormally due to current surges and thus improves thecompatibility of LED lighting system with TRIAC dimmer.

In certain embodiments, a system for LED switch control is provided. Forexample, the system includes a rectifying module configured to rectifyan input voltage that has been processed by a TRIAC dimmer and totransmit the rectified voltage to a combination of one or more LEDs, thecombination of the one or more LEDs being coupled to a constant currentmodule and an enablement control module. As an example, the system alsoincludes the enablement control module configured to receive a sensingvoltage corresponding to the rectified voltage, to compare the sensingvoltage with a predetermined threshold voltage, to output an enablementsignal at a logic low level if the sensing voltage is lower than thepredetermined threshold voltage, and to output the enablement signal ata logic high level if the sensing voltage is higher than thepredetermined threshold voltage. As an example, the system also includesthe constant current module configured to receive the enablement signal,to allow a current to flow through the combination of the one or moreLEDs if the enablement signal is at the logic high level, and to notallow the current to flow through the combination of the one or moreLEDs if the enablement signal is at the logic low level. In someembodiments, an LED lighting system including an LED switch controlsystem is provided.

According to certain embodiments, a system for controlling one or morelight emitting diodes includes a current regulation circuit coupled to acathode of one or more light emitting diodes. The one or more lightemitting diodes include the cathode and an anode configured to receive arectified voltage. Additionally, the system includes a control circuitcoupled to the cathode of the one or more light emitting diodes. Thecontrol circuit is configured to receive a first voltage from thecathode of the one or more light emitting diodes, compare a secondvoltage and a threshold voltage, and generate a control signal based atleast in part on the second voltage and the threshold voltage. Thesecond voltage indicates a magnitude of the first voltage. The controlcircuit is further configured to: if the second voltage is larger thanthe threshold voltage, generate the control signal at a first logiclevel; and if the second voltage is smaller than the threshold voltage,generate the control signal at a second logic level. The currentregulation circuit is configured to: receive the control signal from thecontrol circuit; allow a current to flow through the one or more lightemitting diodes if the control signal is at the first logic level, thecurrent being larger than zero in magnitude; and not allow the currentto flow through the one or more light emitting diodes if the controlsignal is at the second logic level.

According to some embodiments, a system for controlling one or morelight emitting diodes includes a current regulation circuit configuredto receive a rectified voltage and coupled to an anode of one or morelight emitting diodes. The one or more light emitting diodes include theanode and a cathode. Additionally, the system includes a control circuitconfigured to receive the rectified voltage. The control circuit isconfigured to: compare an input voltage and a threshold voltage, theinput voltage indicating a magnitude of the rectified voltage; andgenerate a control signal based at least in part on the input voltageand the threshold voltage. The control circuit is further configured to:if the input voltage is larger than the threshold voltage, generate thecontrol signal at a first logic level; and if the input voltage issmaller than the threshold voltage, generate the control signal at asecond logic level. The current regulation circuit is configured to:receive the control signal from the control circuit; allow a current toflow through the one or more light emitting diodes if the control signalis at the first logic level, the current being larger than zero inmagnitude; and not allow the current to flow through the one or morelight emitting diodes if the control signal is at the second logiclevel.

According to certain embodiments, a method for controlling one or morelight emitting diodes includes: receiving a first voltage from a cathodeof one or more light emitting diodes by a control circuit coupled to thecathode of the one or more light emitting diodes, the one or more lightemitting diodes including the cathode and an anode configured to receivea rectified voltage; comparing a second voltage and a threshold voltage,the second voltage indicating a magnitude of the first voltage;generating a control signal at a first logic level if the second voltageis larger than the threshold voltage; generating the control signal at asecond logic level if the second voltage is smaller than the thresholdvoltage; receiving the control signal from the control circuit by acurrent regulation circuit coupled to the cathode of one or more lightemitting diodes; allowing a current to flow through the one or morelight emitting diodes if the control signal is at the first logic level,the current being larger than zero in magnitude; and not allowing thecurrent to flow through the one or more light emitting diodes if thecontrol signal is at the second logic level.

According to some embodiments, a method for controlling one or morelight emitting diodes includes: receiving a rectified voltage by acontrol circuit; comparing an input voltage and a threshold voltage, theinput voltage indicating a magnitude of the rectified voltage; if theinput voltage is larger than the threshold voltage, generating a controlsignal at a first logic level; if the input voltage is smaller than thethreshold voltage, generating the control signal at a second logiclevel; receiving the control signal from the control circuit by acurrent regulation circuit configured to receive the rectified voltageand coupled to an anode of one or more light emitting diodes, the one ormore light emitting diodes including the anode and a cathode; allowing acurrent to flow through the one or more light emitting diodes if thecontrol signal is at the first logic level, the current being largerthan zero in magnitude; and not allowing the current to flow through theone or more light emitting diodes if the control signal is at the secondlogic level.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary circuit diagram showing a conventional linearconstant current LED lighting system with a Triode for AlternatingCurrent (TRIAC) dimmer.

FIG. 2 shows simplified conventional timing diagrams for the LEDlighting system as shown in FIG. 1.

FIG. 3 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to some embodiments of the presentinvention.

FIG. 4 shows simplified timing diagrams for controlling the LED lightingsystem 400 as shown in FIG. 3 according to some embodiments of thepresent invention.

FIG. 5 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to certain embodiments of the presentinvention.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

5. DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the present invention are directed to circuits.More particularly, some embodiments of the invention provide lightingsystems and methods with Triode for Alternating Current (TRIAC) dimmers.Merely by way of example, some embodiments of the invention have beenapplied to light emitting diodes (LEDs). But it would be recognized thatthe invention has a much broader range of applicability.

FIG. 3 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to some embodiments of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 3, the LED lighting system 400 includes a line (L) terminal and aneutral (N) terminal, and the system 400 also includes a TRIAC dimmer390, a full-wave rectifying bridge 392 (e.g., a full-wave rectifyingbridge BD1), a fuse 394, and a system controller 300. In some examples,the system controller 300 includes a constant current circuit 310 and acontrol circuit 320 (e.g., an enablement control circuit). For example,the system controller 300 is located on a chip. As an example, theconstant current circuit 310 includes an amplifier 330 (e.g., an erroramplifier U1), a transistor 332 (e.g., a transistor M1 for powerregulation), and a resistor 334 (e.g., a sensing resistor R1). Forexample, the control circuit 320 includes a resistor 340 (e.g., aresistor R2), a resistor 342 (e.g., a resistor R3), a comparator 344(e.g., a comparator U2), and a switch 346 (e.g., a switch SW1). Incertain examples, the LED lighting system 400 provides a current 305(e.g., an LED current I_(led)) that flows through one or more LEDs 490,the transistor 332 (e.g., the transistor M1 for power regulation), andthe resistor 334 (e.g., the sensing resistor R1). For example, one ormore LEDs 490 include multiple LEDs connected in series. Although theabove has been shown using a selected group of components for the LEDlighting system, there can be many alternatives, modifications, andvariations. For example, some of the components may be expanded and/orcombined. Other components may be inserted to those noted above.Depending upon the embodiment, the arrangement of components may beinterchanged with others replaced. Further details of these componentsare found throughout the present specification.

In certain embodiments, an AC input voltage (e.g., VAC) is received bythe TRIAC dimmer 390 and also rectified (e.g., by the full-waverectifying bridge 392) to generate a rectified voltage 301 (e.g., arectified voltage V_(bulk)). For example, the full-wave rectifyingbridge 392 is coupled to the TRIAC dimmer 390 through the fuse 394. Asan example, the rectified voltage 301 does not fall below the groundvoltage of the system (e.g., zero volt). In some embodiments, thetransistor 332 (e.g., the transistor M1 for power regulation) includes asource terminal 350, a gate terminal 352 and a drain terminal 354, theamplifier 330 (e.g., the error amplifier U1) includes input terminals356 and 358 and an output terminal 360, and the resistor 334 (e.g., thesensing resistor R1) includes terminals 362 and 364. For example, thesource terminal 350 of the transistor 332 is connected to the terminal362 of the resistor 334, the gate terminal 352 of the transistor 332 isconnected to the output terminal 360 of the amplifier 330, and the drainterminal 354 of the transistor 332 is connected to a cathode of the oneor more LEDs 490. As an example, an anode of the one or more LEDs 490receives the rectified voltage 301 (e.g., a rectified voltage V_(bulk)),and the terminal 364 of the resistor 334 is biased to the ground voltageof the system (e.g., zero volt).

According to certain embodiments, the resistor 340 (e.g., the resistorR2) includes terminals 366 and 368, the resistor 342 (e.g., the resistorR3) includes terminals 370 and 372, and the comparator 344 (e.g., thecomparator U2) includes an input terminal 374 (e.g., a non-invertingterminal), an input terminal 376 (e.g., an inverting terminal), and anoutput terminal 378. For example, the terminal 366 of the resistor 340is connected to the drain terminal 354 of the transistor 332, and theterminal 372 of the resistor 342 is biased to the ground voltage of thesystem (e.g., zero volt). As an example, the terminal 368 of theresistor 340 and the terminal 370 of the resistor 342 are connected at anode 380 (e.g., a node DS), and the node 380 (e.g., the node DS) isconnected to the input terminal 374 of the comparator 344. For example,the input terminal 374 of the comparator 344 is configured to detect achange of a voltage 333 of the drain terminal 354 of the transistor 332.

According to some embodiments, the input terminal 374 (e.g., thepositive terminal) of the comparator 344 receives a voltage 375 of thenode 380 (e.g., the node DS), which is connected to the terminal 368 ofthe resistor 340 and the terminal 370 of the resistor 342. For example,the voltage 375 is directly proportional to the voltage 333 of the drainterminal 354 of the transistor 332. As an example, the input terminal376 (e.g., the negative terminal) of the comparator 344 receives athreshold voltage 377 (e.g., a threshold voltage V_(th)).

In certain embodiments, the comparator 344 compares the voltage 375 andthe threshold voltage 377 and generates a control signal 379 (e.g., acontrol signal en). For example, if the voltage 375 is larger than thethreshold voltage 377, the control signal 379 is at a logic high level.As an example, if the voltage 375 is smaller than the threshold voltage377, the control signal 379 is at a logic low level. In someembodiments, the comparator 344 outputs the control signal 379 at theoutput terminal 378, and sends the control signal 379 to the switch 346(e.g., the switch SW1) of the constant current circuit 310.

In some embodiments, the switch 346 includes terminals 382 and 384. Forexample, the terminal 382 is connected to the output terminal 360 of theamplifier 330, and the terminal 384 is biased to the ground voltage ofthe system (e.g., zero volt). As an example, the switch 346 receives thecontrol signal 379. In certain examples, if the control signal 379 is atthe logic high level, the switch 346 is open. For example, if the switch346 is open, the constant current circuit 310 is enabled. As an example,if the switch 346 is open, a voltage 303 (e.g., a voltage Gate) of thegate terminal 352 of the transistor 332 is generated by the amplifier330 (e.g., the error amplifier U1). In some examples, if the controlsignal 379 is at the logic low level, the switch 346 is closed. As anexample, if the switch 346 is closed, the constant current circuit 310is disabled. For example, if the switch 346 is closed, the voltage 303of the gate terminal 352 of the transistor 332 is biased to the groundvoltage of the system (e.g., zero volt).

According to some embodiments, if the voltage 375 is smaller than thethreshold voltage 377, the constant current circuit 310 is disabled bythe control signal 379. For example, if the voltage 375 is smaller thanthe threshold voltage 377, the voltage 333 of the drain terminal 354 ofthe transistor 332 is too low for the LED lighting system 400 to providea constant current to the one or more LEDs 490. As an example, if theconstant current circuit 310 is disabled, the current 305 (e.g., the LEDcurrent I_(led)) that flows through the one or more LEDs 490 is equal tozero in magnitude. For example, if the voltage 375 is smaller than thethreshold voltage 377, the constant current circuit 310 does not allowthe current 305 (e.g., the LED current I_(led)) with a magnitude largerthan zero to flow through the one or more LEDs 490.

According to certain embodiments, if the voltage 375 is larger than thethreshold voltage 377, the constant current circuit 310 is enabled bythe control signal 379. As an example, if the voltage 375 is larger thanthe threshold voltage 377, the voltage 333 of the drain terminal 354 ofthe transistor 332 is high enough for the LED lighting system 400 toprovide a constant current to the one or more LEDs 490. For example, ifthe voltage 375 is larger than the threshold voltage 377, the voltage333 of the drain terminal 354 of the transistor 332 is higher than theminimum voltage value that is needed for the LED lighting system 400 toprovide a constant current to the one or more LEDs 490. As an example,if the constant current circuit 310 is enabled, the current 305 thatflows through the one or more LEDs 490 is equal to a constant that islarger than zero in magnitude. For example, if the voltage 375 is largerthan the threshold voltage 377, the constant current circuit 310 allowsthe current 305 (e.g., the LED current I_(led)) with a magnitude largerthan zero to flow through the one or more LEDs 490.

As shown in FIG. 3, the amplifier 330 includes the input terminal 356(e.g., a non-inverting terminal), the input terminal 358 (e.g., aninverting terminal), and the output terminal 360, according to oneembodiment. In some examples, the input terminal 356 (e.g., the positiveterminal) receives a reference voltage 357 (e.g., a reference voltageV_(ref)). In certain examples, the input terminal 358 (e.g., thenegative terminal) is connected to the source terminal 350 of thetransistor 332 and the terminal 362 of the resistor 334, and receives avoltage 359 (e.g., a voltage V_(sense)). For example, the terminal 364of the resistor 334 is biased to the ground voltage of the system (e.g.,zero volt), and the voltage 359 at the terminal 362 of the resistor 334corresponds to the current 305 that flows through the one or more LEDs490. As an example, if the switch 346 is open, the amplifier 330 (e.g.,the error amplifier U1) generates the voltage 303 based at least in parton the reference voltage 357 (e.g., the reference voltage V_(ref)) andthe voltage 359 (e.g., the voltage V_(sense)), and outputs the voltage303 at the output terminal 360. For example, the voltage 303 is receivedby the gate terminal 352 of the transistor 332.

In some embodiments, after the constant current circuit 310 becomesenabled by the control signal 379, the voltage 303 of the gate terminal352 generated by the amplifier 330 (e.g., the error amplifier U1) slowlyincreases from the ground voltage of the system (e.g., zero volt) to adesired voltage value, and the current 305 that flows through the one ormore LEDs 490 also slowly increases from zero to a desired currentvalue. For example, the voltage 303 slowly increases from the groundvoltage of the system (e.g., zero volt) to the desired voltage valuewithout overshoot and/or oscillation. As an example, the current 305slowly increases from zero to the desired current value withoutovershoot and/or oscillation.

In certain embodiments, as shown in FIG. 3, the transistor 332 (e.g.,the transistor M1 for power regulation) is a field effect transistor(e.g., a metal-oxide-semiconductor field effect transistor (MOSFET)).For example, the transistor 332 is an insulated gate bipolar transistor(IGBT). As an example, the transistor 332 is a bipolar junctiontransistor. In some examples, the system controller 300 includes morecomponents or less components. In certain examples, the value of thereference voltage 357 (e.g., the reference voltage V_(ref)) and/or thevalue of the threshold voltage 377 (e.g., the threshold voltage V_(th))can be set as desired by those skilled in the art.

FIG. 4 shows simplified timing diagrams for controlling the LED lightingsystem 400 as shown in FIG. 3 according to some embodiments of thepresent invention. These diagrams are merely examples, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Thewaveform 410 represents the rectified voltage V_(bulk) (e.g., therectified voltage 301) as a function of time, the waveform 420represents the voltage 375 of the node DS (e.g., the node 380) as afunction of time, the waveform 430 represents the control signal en(e.g., the control signal 379) as a function of time, the waveform 440represents the voltage Gate (e.g., the voltage 303) as a function oftime, and the waveform 430 represents the LED current Led (e.g., thecurrent 305) as a function of time. According to some embodiments, thetime period from time t₁₁ to time t₁₅ represents a half cycle of the ACinput voltage (e.g., VAC). For example, the time period from time t₁₁ totime t₁₅ is equal to half a period of the AC input voltage (e.g., VAC).

According to certain embodiments, after the system 400 is powered on,the AC input voltage (e.g., VAC) is received by the TRIAC dimmer 390 andsubjected to a full-wave rectification process performed by thefull-wave rectifying bridge 392 (e.g., the full-wave rectifying bridgeBD1) to generate the rectified voltage 301 (e.g., the rectified voltageV_(bulk)). According to some embodiments, at time t₁₁, the TRIAC dimmer390 enters an on cycle, during which, the TRIAC dimmer 390 does not clipthe AC input voltage (e.g., VAC). For example, at time t₁₁, therectified voltage 301 (e.g., the rectified voltage V_(bulk)) increasesrapidly as shown by the waveform 410.

In some examples, if the rectified voltage 301 (e.g., the rectifiedvoltage V_(bulk)) becomes larger than a magnitude that is needed toprovide a minimum forward operating voltage to the one or more LEDs 490,the rectified voltage 301 (e.g., the rectified voltage V_(bulk)) causesthe voltage 333 of the drain terminal 354 of the transistor 332 toincrease. In certain examples, the voltage 333 is received by a voltagedivider including the resistor 340 (e.g., the resistor R2) and theresistor 342 (e.g., the resistor R3), and the voltage divider generatesthe voltage 375. As an example, if the voltage 333 of the drain terminal354 of the transistor 332 increases, the voltage 375 of the node 380(e.g., the node DS) also increases.

According to certain embodiments, at time t₁₁, the TRIAC dimmer 390stops clipping the AC input voltage (e.g., VAC), and the voltage 375 ofthe node 380 (e.g., the node DS) starts to increase but remains smallerthan the threshold voltage 377 (e.g., the threshold voltage V_(th)) asshown by the waveform 420. For example, at time t₁₁, the voltage 375remains smaller than the threshold voltage 377 as shown by the waveform420, the control signal 379 (e.g., the control signal en) remains at thelogic low level as shown by the waveform 430, and the voltage 303 (e.g.,the voltage Gate) of the gate terminal 352 of the transistor 332 remainsbiased to the ground voltage of the system (e.g., zero volt) as shown bythe waveform 440. As an example, at time t₁₁, the constant currentcircuit 310 remains disabled by the control signal 379, and the current305 (e.g., the LED current I_(led)) remains equal to zero in magnitudeas shown by the waveform 450.

According to some embodiments, from time t₁₁ to time t₁₂, the voltage375 of the node 380 (e.g., the node DS) increases but remains smallerthan the threshold voltage 377 (e.g., the threshold voltage V_(th)) asshown by the waveform 420. For example, from time t₁₁ to time t₁₂, thevoltage 375 remains smaller than the threshold voltage 377 as shown bythe waveform 420, the control signal 379 (e.g., the control signal en)remains at the logic low level as shown by the waveform 430, and thevoltage 303 (e.g., the voltage Gate) of the gate terminal 352 of thetransistor 332 remains biased to the ground voltage of the system (e.g.,zero volt) as shown by the waveform 440. As an example, from time t₁₁ totime t₁₂, the constant current circuit 310 remains disabled by thecontrol signal 379, and the current 305 (e.g., the LED current I_(led))remains equal to zero in magnitude as shown by the waveform 450.

According to certain embodiments, at time t₁₂, the voltage 375 of thenode 380 (e.g., the node DS) becomes larger than the threshold voltage377 (e.g., the threshold voltage V_(th)) as shown by the waveform 420.For example, at time t₁₂, the voltage 375 becomes larger than thethreshold voltage 377 as shown by the waveform 420, the control signal379 (e.g., the control signal en) changes from the logic low level tothe logic high level as shown by the waveform 430, and the voltage 303(e.g., the voltage Gate) of the gate terminal 352 of the transistor 332starts to increase from the ground voltage of the system (e.g., zerovolt) as shown by the waveform 440. As an example, at time t₁₂, theconstant current circuit 310 becomes enabled by the control signal 379,and the current 305 (e.g., the LED current I_(led)) starts to increasefrom zero in magnitude as shown by the waveform 450.

According to some embodiments, from time t₁₂ to time t₁₃, the voltage375 of the node 380 (e.g., the node DS) remains larger than thethreshold voltage 377 (e.g., the threshold voltage V_(th)) as shown bythe waveform 420. In certain examples, from time t₁₂ to time t₁₃, thevoltage 375 remains larger than the threshold voltage 377 as shown bythe waveform 420, the control signal 379 (e.g., the control signal en)remains at the logic high level as shown by the waveform 430, and thevoltage 303 (e.g., the voltage Gate) of the gate terminal 352 of thetransistor 332 increases from the ground voltage of the system (e.g.,zero volt) to a voltage level V₁₁, as shown by the waveform 440. Forexample, the voltage level V₁₁ is higher than a threshold voltage of thegate terminal for turning on the transistor 332 (e.g., the transistor M1for power regulation). In some examples, from time t₁₂ to time t₁₃, theconstant current circuit 310 remains enabled by the control signal 379,and the current 305 (e.g., the LED current I_(led)) increases from zeroto a current level I₁₁ as shown by the waveform 450. As an example, thecurrent level I₁₁ is a predetermined magnitude.

According to certain embodiments, at time t₁₃, the voltage 375 of thenode 380 (e.g., the node DS) remains larger than the threshold voltage377 (e.g., the threshold voltage V_(th)) as shown by the waveform 420.In certain examples, at time t₁₃, the voltage 375 remains larger thanthe threshold voltage 377 as shown by the waveform 420, the controlsignal 379 (e.g., the control signal en) remains at the logic high levelas shown by the waveform 430, and the voltage 303 (e.g., the voltageGate) of the gate terminal 352 of the transistor 332 reaches the voltagelevel V₁₁, as shown by the waveform 440. In some examples, at time t₁₃,the constant current circuit 310 remains enabled by the control signal379, and the current 305 (e.g., the LED current I_(led)) reaches thecurrent level I₁₁ as shown by the waveform 450.

According to some embodiments, from time t₁₃ to time t₁₄, the voltage375 of the node 380 (e.g., the node DS) remains larger than thethreshold voltage 377 (e.g., the threshold voltage V_(th)) as shown bythe waveform 420. In certain examples, from time t₁₃ to time t₁₄, thevoltage 375 remains larger than the threshold voltage 377 as shown bythe waveform 420, the control signal 379 (e.g., the control signal en)remains at the logic high level as shown by the waveform 430, and thevoltage 303 (e.g., the voltage Gate) of the gate terminal 352 of thetransistor 332 remains constant at the voltage level V₁₁, as shown bythe waveform 440. In some examples, from time t₁₃ to time t₁₄, theconstant current circuit 310 remains enabled by the control signal 379,and the current 305 (e.g., the LED current I_(led)) remains constant atthe current level I₁₁ as shown by the waveform 450.

According to certain embodiments, at time t₁₄, the voltage 375 of thenode 380 (e.g., the node DS) becomes smaller than the threshold voltage377 (e.g., the threshold voltage V_(th)) as shown by the waveform 420.For example, at time t₁₄, the voltage 375 becomes smaller than thethreshold voltage 377 as shown by the waveform 420, the control signal379 (e.g., the control signal en) changes from the logic high level tothe logic low level as shown by the waveform 430, and the voltage 303(e.g., the voltage Gate) of the gate terminal 352 of the transistor 332decreases from the voltage level V₁₁ to the ground voltage of the system(e.g., zero volt) as shown by the waveform 440. As an example, at timet₁₄, the constant current circuit 310 becomes disabled by the controlsignal 379, and the current 305 (e.g., the LED current I_(led))decreases from the current level I₁₁ to zero as shown by the waveform450.

According to some embodiments, from time t₁₄ to time t₁₅, the voltage375 of the node 380 (e.g., the node DS) remains smaller than thethreshold voltage 377 (e.g., the threshold voltage V_(th)) as shown bythe waveform 420. For example, from time t₁₄ to time t₁₅, the voltage375 remains smaller than the threshold voltage 377 as shown by thewaveform 420, the control signal 379 (e.g., the control signal en)remains at the logic low level as shown by the waveform 430, and thevoltage 303 (e.g., the voltage Gate) of the gate terminal 352 of thetransistor 332 remains at the ground voltage of the system (e.g., zerovolt) as shown by the waveform 440. As an example, from time t₁₄ to timet₁₅, the constant current circuit 310 remains disabled by the controlsignal 379, and the current 305 (e.g., the LED current I_(led)) remainsat zero as shown by the waveform 450.

FIG. 5 is a simplified circuit diagram showing an LED lighting systemwith a TRIAC dimmer according to certain embodiments of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. As shown inFIG. 5, the LED lighting system 600 includes a line (L) terminal and aneutral (N) terminal, and the system 600 also includes a TRIAC dimmer590, a full-wave rectifying bridge 592 (e.g., a full-wave rectifyingbridge BD1), a fuse 594, and a system controller 500. In some examples,the system controller 500 includes a constant current circuit 510 and acontrol circuit 520 (e.g., an enablement control circuit). For example,the system controller 500 is located on a chip. As an example, theconstant current circuit 510 includes an amplifier 530 (e.g., an erroramplifier U1), a transistor 532 (e.g., a transistor M1 for powerregulation), and a resistor 534 (e.g., a sensing resistor R1). Forexample, the control circuit 520 includes a resistor 540 (e.g., aresistor R2), a resistor 542 (e.g., a resistor R3), a comparator 544(e.g., a comparator U2), and a switch 546 (e.g., a switch SW1). Incertain examples, the LED lighting system 400 provides a current 505(e.g., an LED current I_(led)) that flows through the transistor 332(e.g., the transistor M1 for power regulation), the resistor 334 (e.g.,the sensing resistor R1), and one or more LEDs 690. For example, one ormore LEDs 690 include multiple LEDs connected in series. Although theabove has been shown using a selected group of components for the LEDlighting system, there can be many alternatives, modifications, andvariations. For example, some of the components may be expanded and/orcombined. Other components may be inserted to those noted above.Depending upon the embodiment, the arrangement of components may beinterchanged with others replaced. Further details of these componentsare found throughout the present specification.

In certain embodiments, an AC input voltage (e.g., VAC) is received bythe TRIAC dimmer 590 and also rectified (e.g., by the full-waverectifying bridge 592) to generate a rectified voltage 501 (e.g., arectified voltage V_(bulk)). For example, the full-wave rectifyingbridge 592 is coupled to the TRIAC dimmer 590 through the fuse 594. Asan example, the rectified voltage 501 does not fall below the groundvoltage of the system (e.g., zero volt). In some embodiments, thetransistor 532 (e.g., the transistor M1 for power regulation) includes asource terminal 550, a gate terminal 552 and a drain terminal 554, theamplifier 530 (e.g., the error amplifier U1) includes input terminals556 and 558 and an output terminal 560, and the resistor 534 (e.g., thesensing resistor R1) includes terminals 562 and 564. For example, thesource terminal 550 of the transistor 532 is connected to the terminal562 of the resistor 534, the gate terminal 552 of the transistor 532 isconnected to the output terminal 560 of the amplifier 530, and the drainterminal 554 of the transistor 532 receives a rectified voltage 501(e.g., a rectified voltage V_(bulk)). As an example, the terminal 564 ofthe resistor 534 is connected to an anode of the one or more LEDs 690,and a cathode of the one or more LEDs 690 is biased to the groundvoltage of the system (e.g., zero volt). For example, the terminal 564of the resistor 534 and the anode of the one or more LEDs 690 are biasedto the ground voltage of the chip (e.g., the floating ground). As anexample, the ground voltage of the chip (e.g., the floating ground) isdifferent from the ground voltage of the system (e.g., zero volt).

According to certain embodiments, the resistor 540 (e.g., the resistorR2) includes terminals 566 and 568, the resistor 542 (e.g., the resistorR3) includes terminals 570 and 572, and the comparator 544 (e.g., thecomparator U2) includes an input terminal 574 (e.g., a non-invertingterminal), an input terminal 576 (e.g., an inverting terminal), and anoutput terminal 578. In some examples, the terminal 566 of the resistor540 is connected to the drain terminal 554 of the transistor 532, andthe terminal 572 of the resistor 542 is biased to a ground voltage ofthe chip (e.g., a floating ground). For example, the ground voltage ofthe chip (e.g., the floating ground) is different from the groundvoltage of the system (e.g., zero volt). As an example, the terminal 568of the resistor 540 and the terminal 570 of the resistor 542 areconnected at a node 580 (e.g., a node DS), and the node 580 (e.g., thenode DS) is connected to the input terminal 574 of the comparator 544.For example, the input terminal 574 of the comparator 544 is configuredto detect a change of a voltage 533 of the drain terminal 554 of thetransistor 532. As an example, the voltage 533 of the drain terminal 554of the transistor 532 is equal to the rectified voltage 501 (e.g., therectified voltage V_(bulk)).

According to some embodiments, the input terminal 574 (e.g., thepositive terminal) of the comparator 544 receives a voltage 575 of thenode 580 (e.g., the node DS), which is connected to the terminal 568 ofthe resistor 540 and the terminal 570 of the resistor 542. For example,the voltage 575 is directly proportional to the voltage 533 of the drainterminal 554 of the transistor 532. As an example, the input terminal576 (e.g., the negative terminal) of the comparator 544 receives athreshold voltage 577 (e.g., a threshold voltage V_(th)).

In certain embodiments, the comparator 544 compares the voltage 575 andthe threshold voltage 577 and generates a control signal 579 (e.g., acontrol signal en). For example, if the voltage 575 is larger than thethreshold voltage 577, the control signal 579 is at a logic high level.As an example, if the voltage 575 is smaller than the threshold voltage577, the control signal 579 is at a logic low level. In someembodiments, the comparator 544 outputs the control signal 579 at theoutput terminal 578, and sends the control signal 579 to the switch 546(e.g., the switch SW1) of the constant current circuit 510.

In some embodiments, the switch 546 includes terminals 582 and 584. Forexample, the terminal 582 is connected to the output terminal 560 of theamplifier 530, and the terminal 584 is biased to the ground voltage ofthe chip (e.g., the floating ground). For example, the ground voltage ofthe chip (e.g., the floating ground) is different from the groundvoltage of the system (e.g., zero volt). As an example, the switch 546receives the control signal 579. In certain examples, if the controlsignal 579 is at the logic high level, the switch 546 is open. Forexample, if the switch 546 is open, the constant current circuit 510 isenabled. As an example, if the switch 546 is open, a voltage 503 (e.g.,a voltage Gate) of the gate terminal 552 of the transistor 532 isgenerated by the amplifier 530 (e.g., the error amplifier U1). In someexamples, if the control signal 579 is at the logic low level, theswitch 546 is closed. As an example, if the switch 546 is closed, theconstant current circuit 510 is disabled. For example, if the switch 546is closed, the voltage 503 of the gate terminal 552 of the transistor532 is biased to the ground voltage of the chip (e.g., the floatingground). As an example, the ground voltage of the chip (e.g., thefloating ground) is different from the ground voltage of the system(e.g., zero volt).

According to some embodiments, if the voltage 575 is smaller than thethreshold voltage 577, the constant current circuit 510 is disabled bythe control signal 579. For example, if the voltage 575 is smaller thanthe threshold voltage 577, the voltage 533 of the drain terminal 554 ofthe transistor 532 is too low for the LED lighting system 600 to providea constant current to the one or more LEDs 690. As an example, if theconstant current circuit 510 is disabled, the current 505 (e.g., the LEDcurrent I_(led)) that flows through the one or more LEDs 690 is equal tozero in magnitude. For example, if the voltage 575 is smaller than thethreshold voltage 577, the constant current circuit 510 does not allowthe current 505 (e.g., the LED current I_(led)) with a magnitude largerthan zero to flow through the one or more LEDs 690.

According to certain embodiments, if the voltage 575 is larger than thethreshold voltage 577, the constant current circuit 510 is enabled bythe control signal 579. As an example, if the voltage 575 is larger thanthe threshold voltage 577, the voltage 533 of the drain terminal 554 ofthe transistor 532 is high enough for the LED lighting system 600 toprovide a constant current to the one or more LEDs 690. For example, ifthe voltage 575 is larger than the threshold voltage 577, the voltage533 of the drain terminal 554 of the transistor 532 is higher than theminimum voltage value that is needed for the LED lighting system 600 toprovide a constant current to the one or more LEDs 690. As an example,if the constant current circuit 510 is enabled, the current 505 thatflows through the one or more LEDs 690 is equal to a constant that islarger than zero in magnitude. For example, if the voltage 575 is largerthan the threshold voltage 577, the constant current circuit 510 allowsthe current 505 (e.g., the LED current Led) with a magnitude larger thanzero to flow through the one or more LEDs 690.

As shown in FIG. 5, the amplifier 530 includes the input terminal 556(e.g., a non-inverting terminal), the input terminal 558 (e.g., aninverting terminal), and the output terminal 560, according to oneembodiment. In some examples, the input terminal 556 (e.g., the positiveterminal) receives a reference voltage 557 (e.g., a reference voltageV_(ref)). In certain examples, the input terminal 558 (e.g., thenegative terminal) is connected to the source terminal 550 of thetransistor 532 and the terminal 562 of the resistor 534, and receives avoltage 559 (e.g., a voltage V_(sense)). For example, the terminal 564of the resistor 534 is connected to the anode of the one or more LEDs690, and the voltage 559 at the terminal 562 of the resistor 534corresponds to the current 505 that flows through the one or more LEDs690. As an example, if the switch 546 is open, the amplifier 530 (e.g.,the error amplifier U1) generates the voltage 503 based at least in parton the reference voltage 557 (e.g., the reference voltage V_(ref)) andthe voltage 559 (e.g., the voltage V_(sense)), and outputs the voltage503 at the output terminal 560. For example, the voltage 503 is receivedby the gate terminal 552 of the transistor 532.

In some embodiments, after the constant current circuit 510 becomesenabled by the control signal 579, the voltage 503 of the gate terminal552 generated by the amplifier 530 (e.g., the error amplifier U1) slowlyincreases from the ground voltage of the chip (e.g., the floatingground) to a desired voltage value, and the current 505 that flowsthrough the one or more LEDs 690 also slowly increases from zero to adesired current value. For example, the voltage 503 slowly increasesfrom the ground voltage of the chip (e.g., the floating ground) to thedesired voltage value without overshoot and/or oscillation. As anexample, the current 505 slowly increases from zero to the desiredcurrent value without overshoot and/or oscillation.

In certain embodiments, as shown in FIG. 5, the transistor 532 (e.g.,the transistor M1 for power regulation) is a field effect transistor(e.g., a metal-oxide-semiconductor field effect transistor (MOSFET)).For example, the transistor 532 is an insulated gate bipolar transistor(IGBT). As an example, the transistor 532 is a bipolar junctiontransistor. In some examples, the system controller 600 includes morecomponents or less components. In certain examples, the value of thereference voltage 557 (e.g., the reference voltage V_(ref)) and/or thevalue of the threshold voltage 577 (e.g., the threshold voltage V_(th))can be set as desired by those skilled in the art.

According to certain embodiments, at time t₂₁, the TRIAC dimmer 590stops clipping the AC input voltage (e.g., VAC), and the voltage 575 ofthe node 580 (e.g., the node DS) starts to increase but remains smallerthan the threshold voltage 577 (e.g., the threshold voltage V_(th)). Forexample, at time t₂₁, the voltage 575 remains smaller than the thresholdvoltage 577, the control signal 579 (e.g., the control signal en)remains at the logic low level, and the voltage 503 (e.g., the voltageGate) of the gate terminal 552 of the transistor 532 remains biased tothe ground voltage of the chip (e.g., the floating ground). As anexample, at time t₂₁, the constant current circuit 510 remains disabledby the control signal 579, and the current 505 (e.g., the LED currentI_(led)) remains equal to zero in magnitude.

According to some embodiments, from time t₂₁ to time t₂₂, the voltage575 of the node 580 (e.g., the node DS) increases but remains smallerthan the threshold voltage 577 (e.g., the threshold voltage V_(th)). Forexample, from time t₂₁ to time t₂₂, the voltage 575 remains smaller thanthe threshold voltage 577, the control signal 579 (e.g., the controlsignal en) remains at the logic low level, and the voltage 503 (e.g.,the voltage Gate) of the gate terminal 552 of the transistor 532 remainsbiased to the ground voltage of the chip (e.g., the floating ground). Asan example, from time t₂₁ to time t₂₂, the constant current circuit 510remains disabled by the control signal 579, and the current 505 (e.g.,the LED current Led) remains equal to zero in magnitude.

According to certain embodiments, at time t₂₂, the voltage 575 of thenode 580 (e.g., the node DS) becomes larger than the threshold voltage577 (e.g., the threshold voltage V_(th)). For example, at time t₂₂, thevoltage 575 becomes larger than the threshold voltage 577, the controlsignal 579 (e.g., the control signal en) changes from the logic lowlevel to the logic high level, and the voltage 503 (e.g., the voltageGate) of the gate terminal 552 of the transistor 532 starts to increasefrom the ground voltage of the chip (e.g., the floating ground). As anexample, at time t₂₂, the constant current circuit 510 becomes enabledby the control signal 579, and the current 505 (e.g., the LED currentI_(led)) starts to increase from zero in magnitude.

According to some embodiments, from time t₂₂ to time t₂₃, the voltage575 of the node 580 (e.g., the node DS) remains larger than thethreshold voltage 577 (e.g., the threshold voltage V_(th)). In certainexamples, from time t₂₂ to time t₂₃, the voltage 575 remains larger thanthe threshold voltage 577, the control signal 579 (e.g., the controlsignal en) remains at the logic high level, and the voltage 503 (e.g.,the voltage Gate) of the gate terminal 552 of the transistor 532increases from the ground voltage of the chip (e.g., the floatingground) to a voltage level V₂₁. For example, the voltage level V₂₁ ishigher than a threshold voltage of the gate terminal for turning on thetransistor 532 (e.g., the transistor M1 for power regulation). In someexamples, from time t₂₂ to time t₂₃, the constant current circuit 510remains enabled by the control signal 579, and the current 505 (e.g.,the LED current I_(led)) increases from zero to a current level I₂₁. Asan example, the current level I₂₁ is a predetermined magnitude.

According to certain embodiments, at time t₂₃, the voltage 575 of thenode 580 (e.g., the node DS) remains larger than the threshold voltage577 (e.g., the threshold voltage V_(th)). In certain examples, at timet₂₃, the voltage 575 remains larger than the threshold voltage 577, thecontrol signal 579 (e.g., the control signal en) remains at the logichigh level, and the voltage 503 (e.g., the voltage Gate) of the gateterminal 552 of the transistor 532 reaches the voltage level V₂₁. Insome examples, at time t₂₃, the constant current circuit 510 remainsenabled by the control signal 579, and the current 505 (e.g., the LEDcurrent I_(led)) reaches the current level I₂₁.

According to some embodiments, from time t₂₃ to time t₂₄, the voltage575 of the node 580 (e.g., the node DS) remains larger than thethreshold voltage 577 (e.g., the threshold voltage V_(th)). In certainexamples, from time t₂₃ to time t₂₄, the voltage 575 remains larger thanthe threshold voltage 577, the control signal 579 (e.g., the controlsignal en) remains at the logic high level, and the voltage 503 (e.g.,the voltage Gate) of the gate terminal 552 of the transistor 532 remainsconstant at the voltage level V₂₁. In some examples, from time t₂₃ totime t₂₄, the constant current circuit 510 remains enabled by thecontrol signal 579, and the current 505 (e.g., the LED current I_(led))remains constant at the current level I₂₁.

According to certain embodiments, at time t₂₄, the voltage 575 of thenode 580 (e.g., the node DS) becomes smaller than the threshold voltage577 (e.g., the threshold voltage V_(th)). For example, at time t₂₄, thevoltage 575 becomes smaller than the threshold voltage 577, the controlsignal 579 (e.g., the control signal en) changes from the logic highlevel to the logic low level, and the voltage 503 (e.g., the voltageGate) of the gate terminal 552 of the transistor 532 decreases from thevoltage level V₂₁ to the ground voltage of the chip (e.g., the floatingground). As an example, at time t₂₄, the constant current circuit 510becomes disabled by the control signal 579, and the current 505 (e.g.,the LED current I_(led)) decreases from the current level I₂₁ to zero.

According to some embodiments, from time t₂₄ to time t₂₅, the voltage575 of the node 580 (e.g., the node DS) remains smaller than thethreshold voltage 577 (e.g., the threshold voltage V_(th)). For example,from time t₂₄ to time t₂₅, the voltage 575 remains smaller than thethreshold voltage 577, the control signal 579 (e.g., the control signalen) remains at the logic low level, and the voltage 503 (e.g., thevoltage Gate) of the gate terminal 552 of the transistor 532 remains atthe ground voltage of the chip (e.g., the floating ground). As anexample, from time t₂₄ to time t₂₅, the constant current circuit 510remains disabled by the control signal 579, and the current 505 (e.g.,the LED current I_(led)) remains at zero.

In certain embodiments, a system for LED switch control is provided. Forexample, the system includes a rectifying module configured to rectifyan input voltage that has been processed by a TRIAC dimmer and totransmit the rectified voltage to a combination of one or more LEDs, thecombination of the one or more LEDs being coupled to a constant currentmodule and an enablement control module. As an example, the system alsoincludes the enablement control module configured to receive a sensingvoltage corresponding to the rectified voltage, to compare the sensingvoltage with a predetermined threshold voltage, to output an enablementsignal at a logic low level if the sensing voltage is lower than thepredetermined threshold voltage, and to output the enablement signal ata logic high level if the sensing voltage is higher than thepredetermined threshold voltage. As an example, the system also includesthe constant current module configured to receive the enablement signal,to allow a current to flow through the combination of the one or moreLEDs if the enablement signal is at the logic high level, and to notallow the current to flow through the combination of the one or moreLEDs if the enablement signal is at the logic low level.

In some examples, the constant current module includes an amplifier, atransistor for power regulation, and a first resistor, wherein thesource of the transistor is coupled to the first resistor, the gate ofthe transistor is coupled to the output of the amplifier, and the drainof the transistor is coupled to a cathode of the combination of the oneor more LEDs. In certain examples, the enablement control moduleincludes a second resistor and a third resistor connected in series, anda comparator, wherein the second resistor and the third resistor areconnected to the drain of the transistor at one end and grounded atanother end, the non-inverting input of the comparator is connected to aconnection point of the first resistor and the second resistor, and theinverting input of the comparator receives the predetermined thresholdvoltage.

According to certain embodiments, a system (e.g., the system controller300) for controlling one or more light emitting diodes includes acurrent regulation circuit (e.g., the constant current circuit 310)coupled to a cathode of one or more light emitting diodes (e.g., the oneor more LEDs 490). The one or more light emitting diodes include thecathode and an anode configured to receive a rectified voltage (e.g.,the rectified voltage 301). Additionally, the system includes a controlcircuit (e.g., the control circuit 320) coupled to the cathode of theone or more light emitting diodes. The control circuit is configured toreceive a first voltage (e.g., the voltage 333) from the cathode of theone or more light emitting diodes, compare a second voltage (e.g., thevoltage 375) and a threshold voltage (e.g., the threshold voltage 377),and generate a control signal (e.g., the control signal 379) based atleast in part on the second voltage and the threshold voltage. Thesecond voltage indicates a magnitude of the first voltage. The controlcircuit is further configured to: if the second voltage is larger thanthe threshold voltage, generate the control signal at a first logiclevel; and if the second voltage is smaller than the threshold voltage,generate the control signal at a second logic level. The currentregulation circuit is configured to: receive the control signal from thecontrol circuit; allow a current (e.g., the current 305) to flow throughthe one or more light emitting diodes if the control signal is at thefirst logic level, the current being larger than zero in magnitude; andnot allow the current to flow through the one or more light emittingdiodes if the control signal is at the second logic level. For example,the system (e.g., the system controller 300) is implemented according toat least FIG. 3.

As an example, the second voltage is directly proportional to the firstvoltage in magnitude. For example, the first logic level is a logic highlevel, and the second logic level is a logic low level. As an example,the current regulation circuit includes: an amplifier (e.g., theamplifier 330) including a first amplifier input terminal (e.g., theinput terminal 356), a second amplifier input terminal (e.g., the inputterminal 358), and an amplifier output terminal (e.g., the outputterminal 360); a transistor (e.g., the transistor 332) including a drainterminal (e.g., the drain terminal 354), a gate terminal (e.g., the gateterminal 352), and a source terminal (e.g., the source terminal 350);and a resistor (e.g., the resistor 334) including a first resistorterminal (e.g., the terminal 362) and a second resistor terminal (e.g.,the terminal 364); wherein: the drain terminal of the transistor iscoupled to the cathode of the one or more light emitting diodes; thegate terminal of the transistor is coupled to the amplifier outputterminal of the amplifier; and the source terminal of the transistor iscoupled to the first resistor terminal of the resistor and the secondamplifier input terminal of the amplifier. For example, the firstamplifier input terminal of the amplifier is configured to receive areference voltage (e.g., the reference voltage 357). As an example, thesecond resistor terminal of the resistor is configured to receive aground voltage (e.g., zero volt).

For example, the control circuit includes: a first resistor (e.g., theresistor 340) including a first resistor terminal (e.g., the terminal366) and a second resistor terminal (e.g., the terminal 368); a secondresistor (e.g., the resistor 342) including a third resistor terminal(e.g., the terminal 370) and a fourth resistor terminal (e.g., theterminal 372), the third resistor terminal being connected to the secondresistor terminal; and a comparator (e.g., the comparator 344) includinga first comparator input terminal (e.g., the input terminal 374), asecond comparator input terminal (e.g., the input terminal 376), and acomparator output terminal (e.g., the output terminal 378); wherein: thefirst resistor terminal is coupled to the cathode of the one or morelight emitting diodes and configured to receive the first voltage; andthe fourth resistor terminal is configured to receive a ground voltage(e.g., zero volt); wherein: the first comparator input terminal iscoupled to the second resistor terminal and the third resistor terminaland configured to receive the second voltage; the second comparatorinput terminal is configured to receive a threshold voltage (e.g., thethreshold voltage 377); and the comparator output terminal is configuredto output the control signal based at least in part on the secondvoltage and the threshold voltage.

As an example, the current regulation circuit includes: an amplifier(e.g., the amplifier 330) including a first amplifier input terminal(e.g., the input terminal 356), a second amplifier input terminal (e.g.,the input terminal 358), and an amplifier output terminal (e.g., theoutput terminal 360); a transistor (e.g., the transistor 332) includinga drain terminal (e.g., the drain terminal 354), a gate terminal (e.g.,the gate terminal 352), and a source terminal (e.g., the source terminal350); and a third resistor (e.g., the resistor 334) including a fifthresistor terminal (e.g., the terminal 362) and a sixth resistor terminal(e.g., the terminal 364); wherein: the drain terminal of the transistoris coupled to the cathode of the one or more light emitting diodes; thegate terminal of the transistor is coupled to the amplifier outputterminal of the amplifier; and the source terminal of the transistor iscoupled to the fifth resistor terminal of the third resistor and thesecond amplifier input terminal of the amplifier. For example, the sixthresistor terminal is configured to receive the ground voltage.

As an example, the control circuit further includes: a switch (e.g., theswitch 346) including a first switch terminal (e.g., the terminal 382)and a second switch terminal (e.g., the terminal 384); wherein: thefirst switch terminal is connected to the amplifier output terminal(e.g., the output terminal 360) of an amplifier (e.g., the amplifier330); and the second switch terminal is configured to receive the groundvoltage. For example, the control circuit is further configured to: openthe switch if the control signal is at the first logic level; and closethe switch if the control signal is at the second logic level.

In some examples, from a first time (e.g., time t₁₁) to a second time(e.g., time t₁₂), the second voltage (e.g., the voltage 375) increasesbut remains smaller than the threshold voltage (e.g., the thresholdvoltage 377), and the control signal remains at the second logic level;at the second time, the second voltage (e.g., the voltage 375) becomeslarger than the threshold voltage (e.g., the threshold voltage 377), andthe control signal changes from the second logic level to the firstlogic level; from the second time (e.g., time t₁₂) to a third time(e.g., time t₁₃), the second voltage remains larger than the thresholdvoltage, and the control signal remains at the first logic level; at thethird time (e.g., time t₁₃), the second voltage remains larger than thethreshold voltage, the control signal remains at the first logic level,and the current (e.g., the current 305) reaches a predetermined currentlevel (e.g., the current level I₁₁); from the third time (e.g., timet₁₃) to a fourth time (e.g., time t₁₄), the second voltage remainslarger than the threshold voltage, the control signal remains at thefirst logic level, and the current (e.g., the current 305) remainsconstant at the predetermined current level (e.g., the current levelI₁₁); at the fourth time (e.g., time t₁₄), the second voltage becomessmaller than the threshold voltage, and the control signal changes fromthe first logic level to the second voltage level; and from the fourthtime (e.g., time t₁₄) to a fifth time (e.g., time t₁₅), the secondvoltage remains smaller than the threshold voltage, and the controlsignal remains at the second voltage level.

According to some embodiments, a system (e.g., the system controller500) for controlling one or more light emitting diodes includes acurrent regulation circuit (e.g., the constant current circuit 510)configured to receive a rectified voltage (e.g., the rectified voltage501) and coupled to an anode of one or more light emitting diodes (e.g.,the one or more LEDs 690). The one or more light emitting diodes includethe anode and a cathode. Additionally, the system includes a controlcircuit (e.g., the control circuit 520) configured to receive therectified voltage (e.g., the rectified voltage 501). The control circuitis configured to: compare an input voltage (e.g., the voltage 575) and athreshold voltage (e.g., the threshold voltage 577), the input voltageindicating a magnitude of the rectified voltage; and generate a controlsignal (e.g., the control signal 579) based at least in part on theinput voltage and the threshold voltage. The control circuit is furtherconfigured to: if the input voltage is larger than the thresholdvoltage, generate the control signal at a first logic level; and if theinput voltage is smaller than the threshold voltage, generate thecontrol signal at a second logic level. The current regulation circuitis configured to: receive the control signal from the control circuit;allow a current (e.g., the current 505) to flow through the one or morelight emitting diodes if the control signal is at the first logic level,the current being larger than zero in magnitude; and not allow thecurrent to flow through the one or more light emitting diodes if thecontrol signal is at the second logic level. For example, the system(e.g., the system controller 500) is implemented according to at leastFIG. 5.

As an example, the input voltage is directly proportional to therectified voltage in magnitude. For example, the first logic level is alogic high level; and the second logic level is a logic low level. As anexample, the current regulation circuit includes: an amplifier (e.g.,the amplifier 530) including a first amplifier input terminal (e.g., theinput terminal 556), a second amplifier input terminal (e.g., the inputterminal 558), and an amplifier output terminal (e.g., the outputterminal 560); a transistor (e.g., the transistor 532) including a drainterminal (e.g., the drain terminal 554), a gate terminal (e.g., the gateterminal 552), and a source terminal (e.g., the source terminal 550);and a resistor (e.g., the resistor 534) including a first resistorterminal (e.g., the terminal 562) and a second resistor terminal (e.g.,the terminal 564); wherein: the drain terminal of the transistor isconfigured to receive the rectified voltage (e.g., the rectified voltage501); the gate terminal of the transistor is coupled to the amplifieroutput terminal of the amplifier; and the source terminal of thetransistor is coupled to the anode of the one or more light emittingdiodes (e.g., the one or more LEDs 690). For example, the firstamplifier input terminal of the amplifier is configured to receive areference voltage (e.g., the reference voltage 557). As an example, thecathode of the one or more light emitting diodes is configured toreceive a ground voltage (e.g., zero volt).

For example, the control circuit includes: a first resistor (e.g., theresistor 540) including a first resistor terminal (e.g., the terminal566) and a second resistor terminal (e.g., the terminal 568); a secondresistor (e.g., the resistor 542) including a third resistor terminal(e.g., the terminal 570) and a fourth resistor terminal (e.g., theterminal 572), the third resistor terminal being connected to the secondresistor terminal; and a comparator (e.g., the comparator 544) includinga first comparator input terminal (e.g., the input terminal 574), asecond comparator input terminal (e.g., the input terminal 576), and acomparator output terminal (e.g., the output terminal 578); wherein: thefirst resistor terminal is configured to receive the rectified voltage(e.g., the rectified voltage 501); and the fourth resistor terminal isconfigured to receive a ground voltage (e.g., the floating ground);wherein: the first comparator input terminal is coupled to the secondresistor terminal and the third resistor terminal and configured toreceive the input voltage; the second comparator input terminal isconfigured to receive a threshold voltage (e.g., the threshold voltage577); and the comparator output terminal is configured to output thecontrol signal based at least in part on the input voltage and thethreshold voltage.

As an example, the current regulation circuit includes: an amplifier(e.g., the amplifier 530) including a first amplifier input terminal(e.g., the input terminal 556), a second amplifier input terminal (e.g.,the input terminal 558), and an amplifier output terminal (e.g., theoutput terminal 560); a transistor (e.g., the transistor 532) includinga drain terminal (e.g., the drain terminal 554), a gate terminal (e.g.,the gate terminal 552), and a source terminal (e.g., the source terminal550); and a third resistor (e.g., the resistor 534) including a fifthresistor terminal (e.g., the terminal 562) and a sixth resistor terminal(e.g., the terminal 564); wherein: the drain terminal of the transistoris configured to receive the rectified voltage (e.g., the rectifiedvoltage 501); the gate terminal of the transistor is coupled to theamplifier output terminal of the amplifier; and the source terminal ofthe transistor is coupled to the fifth resistor terminal of the thirdresistor and the second amplifier input terminal of the amplifier. Forexample, the sixth resistor terminal is coupled to the anode of the oneor more light emitting diodes.

As an example, the control circuit further includes: a switch (e.g., theswitch 546) including a first switch terminal (e.g., the terminal 582)and a second switch terminal (e.g., the terminal 584); wherein: thefirst switch terminal is connected to the amplifier output terminal(e.g., the output terminal 560) of an amplifier (e.g., the amplifier530); and the second switch terminal is configured to receive the groundvoltage. For example, the control circuit is further configured to: openthe switch if the control signal is at the first logic level; and closethe switch if the control signal is at the second logic level.

In certain examples, from a first time (e.g., time t₂₁) to a second time(e.g., time t₂₂), the second voltage (e.g., the voltage 575) increasesbut remains smaller than the threshold voltage (e.g., the thresholdvoltage 577), and the control signal remains at the second logic level;at the second time, the second voltage (e.g., the voltage 575) becomeslarger than the threshold voltage (e.g., the threshold voltage 577), andthe control signal changes from the second logic level to the firstlogic level; from the second time (e.g., time t₂₂) to a third time(e.g., time t₂₃), the second voltage remains larger than the thresholdvoltage, and the control signal remains at the first logic level; at thethird time (e.g., time t₂₃), the second voltage remains larger than thethreshold voltage, the control signal remains at the first logic level,and the current (e.g., the current 505) reaches a predetermined currentlevel (e.g., the current level I₂₁); from the third time (e.g., timet₂₃) to a fourth time (e.g., time t₂₄), the second voltage remainslarger than the threshold voltage, the control signal remains at thefirst logic level, and the current (e.g., the current 505) remainsconstant at the predetermined current level (e.g., the current levelI₂₁); at the fourth time (e.g., time t₂₄), the second voltage becomessmaller than the threshold voltage, and the control signal changes fromthe first logic level to the second voltage level; and from the fourthtime (e.g., time t₂₄) to a fifth time (e.g., time t₂₅), the secondvoltage remains smaller than the threshold voltage, and the controlsignal remains at the second voltage level.

According to certain embodiments, a method for controlling one or morelight emitting diodes includes: receiving a first voltage (e.g., thevoltage 333) from a cathode of one or more light emitting diodes by acontrol circuit (e.g., the control circuit 320) coupled to the cathodeof the one or more light emitting diodes, the one or more light emittingdiodes including the cathode and an anode configured to receive arectified voltage (e.g., the rectified voltage 301); comparing a secondvoltage (e.g., the voltage 375) and a threshold voltage (e.g., thethreshold voltage 377), the second voltage indicating a magnitude of thefirst voltage; generating a control signal (e.g., the control signal379) at a first logic level if the second voltage is larger than thethreshold voltage; generating the control signal at a second logic levelif the second voltage is smaller than the threshold voltage; receivingthe control signal from the control circuit by a current regulationcircuit (e.g., the constant current circuit 310) coupled to the cathodeof one or more light emitting diodes (e.g., the one or more LEDs 490);allowing a current (e.g., the current 305) to flow through the one ormore light emitting diodes if the control signal is at the first logiclevel, the current being larger than zero in magnitude; and not allowingthe current to flow through the one or more light emitting diodes if thecontrol signal is at the second logic level. For example, the method isimplemented according to at least FIG. 3.

According to some embodiments, a method for controlling one or morelight emitting diodes includes: receiving a rectified voltage (e.g., therectified voltage 501) by a control circuit (e.g., the control circuit520); comparing an input voltage (e.g., the voltage 575) and a thresholdvoltage (e.g., the threshold voltage 577), the input voltage indicatinga magnitude of the rectified voltage; if the input voltage is largerthan the threshold voltage, generating a control signal (e.g., thecontrol signal 579) at a first logic level; if the input voltage issmaller than the threshold voltage, generating the control signal at asecond logic level; receiving the control signal from the controlcircuit by a current regulation circuit (e.g., the constant currentcircuit 510) configured to receive the rectified voltage (e.g., therectified voltage 501) and coupled to an anode of one or more lightemitting diodes (e.g., the one or more LEDs 690), the one or more lightemitting diodes including the anode and a cathode; allowing a current(e.g., the current 505) to flow through the one or more light emittingdiodes if the control signal is at the first logic level, the currentbeing larger than zero in magnitude; and not allowing the current toflow through the one or more light emitting diodes if the control signalis at the second logic level. For example, the method is implementedaccording to at least FIG. 5.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. As an example, some orall components of various embodiments of the present invention each are,individually and/or in combination with at least another component,implemented in one or more circuits, such as one or more analog circuitsand/or one or more digital circuits. For example, various embodimentsand/or examples of the present invention can be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system for controlling one or more lightemitting diodes, the system comprising: a current regulation circuitcoupled to a cathode of one or more light emitting diodes, the one ormore light emitting diodes including the cathode and an anode configuredto receive a rectified voltage; a control circuit coupled to the cathodeof the one or more light emitting diodes; wherein the control circuit isconfigured to: receive a first voltage from the cathode of the one ormore light emitting diodes; compare a second voltage and a thresholdvoltage, the second voltage indicating a magnitude of the first voltage;and generate a control signal based at least in part on the secondvoltage and the threshold voltage; wherein the control circuit isfurther configured to: if the second voltage is larger than thethreshold voltage, generate the control signal at a first logic level;and if the second voltage is smaller than the threshold voltage,generate the control signal at a second logic level; wherein the currentregulation circuit is configured to: receive the control signal from thecontrol circuit; allow a current to flow through the one or more lightemitting diodes if the control signal is at the first logic level, thecurrent being larger than zero in magnitude; and not allow the currentto flow through the one or more light emitting diodes if the controlsignal is at the second logic level.
 2. The system of claim 1 whereinthe second voltage is directly proportional to the first voltage inmagnitude.
 3. The system of claim 1 wherein: the first logic level is alogic high level; and the second logic level is a logic low level. 4.The system of claim 1 wherein the current regulation circuit includes:an amplifier including a first amplifier input terminal, a secondamplifier input terminal, and an amplifier output terminal; a transistorincluding a drain terminal, a gate terminal, and a source terminal; anda resistor including a first resistor terminal and a second resistorterminal; wherein: the drain terminal of the transistor is coupled tothe cathode of the one or more light emitting diodes; the gate terminalof the transistor is coupled to the amplifier output terminal of theamplifier; and the source terminal of the transistor is coupled to thefirst resistor terminal of the resistor and the second amplifier inputterminal of the amplifier.
 5. The system of claim 4 wherein the firstamplifier input terminal of the amplifier is configured to receive areference voltage.
 6. The system of claim 4 wherein the second resistorterminal of the resistor is configured to receive a ground voltage. 7.The system of claim 1 wherein the control circuit includes: a firstresistor including a first resistor terminal and a second resistorterminal; a second resistor including a third resistor terminal and afourth resistor terminal, the third resistor terminal being connected tothe second resistor terminal; and a comparator including a firstcomparator input terminal, a second comparator input terminal, and acomparator output terminal; wherein: the first resistor terminal iscoupled to the cathode of the one or more light emitting diodes andconfigured to receive the first voltage; and the fourth resistorterminal is configured to receive a ground voltage; wherein: the firstcomparator input terminal is coupled to the second resistor terminal andthe third resistor terminal and configured to receive the secondvoltage; the second comparator input terminal is configured to receive athreshold voltage; and the comparator output terminal is configured tooutput the control signal based at least in part on the second voltageand the threshold voltage.
 8. The system of claim 7 wherein the currentregulation circuit includes: an amplifier including a first amplifierinput terminal, a second amplifier input terminal, and an amplifieroutput terminal; a transistor including a drain terminal, a gateterminal, and a source terminal; and a third resistor including a fifthresistor terminal and a sixth resistor terminal; wherein: the drainterminal of the transistor is coupled to the cathode of the one or morelight emitting diodes; the gate terminal of the transistor is coupled tothe amplifier output terminal of the amplifier; and the source terminalof the transistor is coupled to the fifth resistor terminal of the thirdresistor and the second amplifier input terminal of the amplifier. 9.The system of claim 8 wherein the sixth resistor terminal is configuredto receive the ground voltage.
 10. The system of claim 8 wherein thecontrol circuit further includes: a switch including a first switchterminal and a second switch terminal; wherein: the first switchterminal is connected to the amplifier output terminal of an amplifier;and the second switch terminal is configured to receive the groundvoltage.
 11. The system of claim 10 wherein the control circuit isfurther configured to: open the switch if the control signal is at thefirst logic level; and close the switch if the control signal is at thesecond logic level.
 12. The system of claim 1 wherein: from a first timeto a second time, the second voltage increases but remains smaller thanthe threshold voltage, and the control signal remains at the secondlogic level; at the second time, the second voltage becomes larger thanthe threshold voltage, and the control signal changes from the secondlogic level to the first logic level; from the second time to a thirdtime, the second voltage remains larger than the threshold voltage, andthe control signal remains at the first logic level; at the third time,the second voltage remains larger than the threshold voltage, thecontrol signal remains at the first logic level, and the current reachesa predetermined current level; from the third time to a fourth time, thesecond voltage remains larger than the threshold voltage, the controlsignal remains at the first logic level, and the current remainsconstant at the predetermined current level; at the fourth time, thesecond voltage becomes smaller than the threshold voltage, and thecontrol signal changes from the first logic level to the second voltagelevel; and from the fourth time to a fifth time, the second voltageremains smaller than the threshold voltage, and the control signalremains at the second voltage level.
 13. A system for controlling one ormore light emitting diodes, the system comprising: a current regulationcircuit configured to receive a rectified voltage and coupled to ananode of one or more light emitting diodes, the one or more lightemitting diodes including the anode and a cathode; a control circuitconfigured to receive the rectified voltage; wherein the control circuitis configured to: compare an input voltage and a threshold voltage, theinput voltage indicating a magnitude of the rectified voltage; andgenerate a control signal based at least in part on the input voltageand the threshold voltage; wherein the control circuit is furtherconfigured to: if the input voltage is larger than the thresholdvoltage, generate the control signal at a first logic level; and if theinput voltage is smaller than the threshold voltage, generate thecontrol signal at a second logic level; wherein the current regulationcircuit is configured to: receive the control signal from the controlcircuit; allow a current to flow through the one or more light emittingdiodes if the control signal is at the first logic level, the currentbeing larger than zero in magnitude; and not allow the current to flowthrough the one or more light emitting diodes if the control signal isat the second logic level.
 14. The system of claim 13 wherein the inputvoltage is directly proportional to the rectified voltage in magnitude.15. The system of claim 13 wherein: the first logic level is a logichigh level; and the second logic level is a logic low level.
 16. Thesystem of claim 13 wherein the current regulation circuit includes: anamplifier including a first amplifier input terminal, a second amplifierinput terminal, and an amplifier output terminal; a transistor includinga drain terminal, a gate terminal, and a source terminal; and a resistorincluding a first resistor terminal and a second resistor terminal;wherein: the drain terminal of the transistor is configured to receivethe rectified voltage; the gate terminal of the transistor is coupled tothe amplifier output terminal of the amplifier; and the source terminalof the transistor is coupled to the anode of the one or more lightemitting diodes.
 17. The system of claim 16 wherein the first amplifierinput terminal of the amplifier is configured to receive a referencevoltage.
 18. The system of claim 16 wherein the cathode of the one ormore light emitting diodes is configured to receive a ground voltage.19. The system of claim 13 wherein the control circuit includes: a firstresistor including a first resistor terminal and a second resistorterminal; a second resistor including a third resistor terminal and afourth resistor terminal, the third resistor terminal being connected tothe second resistor terminal; and a comparator including a firstcomparator input terminal, a second comparator input terminal, and acomparator output terminal; wherein: the first resistor terminal isconfigured to receive the rectified voltage; and the fourth resistorterminal is configured to receive a ground voltage; wherein: the firstcomparator input terminal is coupled to the second resistor terminal andthe third resistor terminal and configured to receive the input voltage;the second comparator input terminal is configured to receive athreshold voltage; and the comparator output terminal is configured tooutput the control signal based at least in part on the input voltageand the threshold voltage.
 20. The system of claim 19 wherein thecurrent regulation circuit includes: an amplifier including a firstamplifier input terminal, a second amplifier input terminal, and anamplifier output terminal; a transistor including a drain terminal, agate terminal, and a source terminal; and a third resistor including afifth resistor terminal and a sixth resistor terminal; wherein: thedrain terminal of the transistor is configured to receive the rectifiedvoltage; the gate terminal of the transistor is coupled to the amplifieroutput terminal of the amplifier; and the source terminal of thetransistor is coupled to the fifth resistor terminal of the thirdresistor and the second amplifier input terminal of the amplifier. 21.The system of claim 20 wherein the sixth resistor terminal is coupled tothe anode of the one or more light emitting diodes.
 22. The system ofclaim 20 wherein the control circuit further includes: a switchincluding a first switch terminal and a second switch terminal; wherein:the first switch terminal is connected to the amplifier output terminalof an amplifier; and the second switch terminal is configured to receivethe ground voltage.
 23. The system of claim 22 wherein the controlcircuit is further configured to: open the switch if the control signalis at the first logic level; and close the switch if the control signalis at the second logic level.
 24. A method for controlling one or morelight emitting diodes, the method comprising: receiving a first voltagefrom a cathode of one or more light emitting diodes by a control circuitcoupled to the cathode of the one or more light emitting diodes, the oneor more light emitting diodes including the cathode and an anodeconfigured to receive a rectified voltage; comparing a second voltageand a threshold voltage, the second voltage indicating a magnitude ofthe first voltage; generating a control signal at a first logic level ifthe second voltage is larger than the threshold voltage; generating thecontrol signal at a second logic level if the second voltage is smallerthan the threshold voltage; receiving the control signal from thecontrol circuit by a current regulation circuit coupled to the cathodeof one or more light emitting diodes; allowing a current to flow throughthe one or more light emitting diodes if the control signal is at thefirst logic level, the current being larger than zero in magnitude; andnot allowing the current to flow through the one or more light emittingdiodes if the control signal is at the second logic level.
 25. A methodfor controlling one or more light emitting diodes, the methodcomprising: receiving a rectified voltage by a control circuit;comparing an input voltage and a threshold voltage, the input voltageindicating a magnitude of the rectified voltage; if the input voltage islarger than the threshold voltage, generating a control signal at afirst logic level; if the input voltage is smaller than the thresholdvoltage, generating the control signal at a second logic level;receiving the control signal from the control circuit by a currentregulation circuit configured to receive the rectified voltage andcoupled to an anode of one or more light emitting diodes, the one ormore light emitting diodes including the anode and a cathode; allowing acurrent to flow through the one or more light emitting diodes if thecontrol signal is at the first logic level, the current being largerthan zero in magnitude; and not allowing the current to flow through theone or more light emitting diodes if the control signal is at the secondlogic level.